In heart muscle cells, the contractile units are linked together by Z bands. Despite their vital role in contraction, the nature and organization of the Z bands are unknown. In the past decade, widened Z bands have been observed in electron micrographs of human cardiac and skeletal muscle. It is not known if this widening of the Z band represents a repair process, a disease process or neither. The purpose of these studies is to determine the organization of Z band components in both normal and widened Z bands and to relate this organization to proposed functions for Z bands in myofibril formation. Optical diffraction analysis combined with electron microscopy has been used successfully by other investigators to study isolated muscle protein crystals. Pilot studies performed in this laboratory on cardiac Z bands show structural and chemical information not readily apparent from the usual direct examination of electron micrographs. Therefore, optical diffraction analysis will be applied to electron micrographs of Z bands in normal, ischemic, anoxic, and hypertrophied mammalian hearts and in fast and slow skeletal muscle. Optical diffraction methods will give new information about Z band structure, chemical composition of the Z band and the relationship of Z components to adjacent thin contractile filaments, and may suggest a mechanism for the formation and breakdown of the Z band. Structural analysis of Z bands in normal, developing and diseased muscle should contribute to our understanding of muscle cell function. BIBLIOGRAPHIC REFERENCES: Entman, M. L., Kaniike, K., Goldstein, M.A., Nelson, T. E., Bornet, E. P., Futch, T. W. and Schwartz, A.: Association of glycogenolysis with cardiac sarcoplasmic reticulum: A possible link between contractility and metabolic control. J. Biol. Chem. 251: 3140-3146, 1976. Goldstein, M. A., Thyrum, P. T., Murphy, D. L., Martin, J. H. and Schwartz, A: Ultrastructural and contractile characteristics of isolated papillary muscle exposed to acute hypoxia. J. Mol. Cell. Cardiol., 1976, in press.